I posted this in the Old's Cool - 2 Smokers section, but I think I can get more help here.

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The past few years I have been slowly trying to get a flat tracker together. I had a TT500, was ready to race (I think), and had an offer to sell. Recently, I bought back my old pile of spare TT/XT parts, thinking I would going to build another one. But, an old family friend of mine wants to help me put a two smoke together. He was a Yamaha mechanic back in the '70's and '80's, and that is what he would like me to build.

So, this is what I would like to do. There is a "local" series, the Classic Flat Track National Championship Series (http://bikedays.com/id52.html), that has a few half mile races a year. Usually, two are held here in Iowa, Davenport and Knoxville. I want to run the V250/360 class. Back in the day (1973 to 1976) that meant 250cc two stroke twins, 360cc two stroke singles, and 360cc four stroke singles and twins. From what I have seen, the Honda XL350 owns the class. I have not seen many smokers. For me that is great, because I would rather be unique.

So, what I am questing for is technical information. I would like to put together a RD250 and a DT/RT/YZ360 powered Champion. Which engine/year/model, for each, was/is the hot setup? The reason I am wanting to build both, is because I think it will be harder to find a Champion frame for the RD, so the DT will probably get built first as I find RD parts. Then, the DT will probably get switched to a short tracker or TT bike.

I posted this in the Old's Cool - 2 Smokers section, but I think I can get more help here.

*** *** *** *** *** *** *** *** ***

The past few years I have been slowly trying to get a flat tracker together. I had a TT500, was ready to race (I think), and had an offer to sell. Recently, I bought back my old pile of spare TT/XT parts, thinking I would going to build another one. But, an old family friend of mine wants to help me put a two smoke together. He was a Yamaha mechanic back in the '70's and '80's, and that is what he would like me to build.

So, this is what I would like to do. There is a "local" series, the Classic Flat Track National Championship Series (http://bikedays.com/id52.html), that has a few half mile races a year. Usually, two are held here in Iowa, Davenport and Knoxville. I want to run the V250/360 class. Back in the day (1973 to 1976) that meant 250cc two stroke twins, 360cc two stroke singles, and 360cc four stroke singles and twins. From what I have seen, the Honda XL350 owns the class. I have not seen many smokers. For me that is great, because I would rather be unique.

So, what I am questing for is technical information. I would like to put together a RD250 and a DT/RT/YZ360 powered Champion. Which engine/year/model, for each, was/is the hot setup? The reason I am wanting to build both, is because I think it will be harder to find a Champion frame for the RD, so the DT will probably get built first as I find RD parts. Then, the DT will probably get switched to a short tracker or TT bike.

Back in the 70's the Champion framed Yamaha Twins used the road racer motors like the TD2 and TD3. The RD 250 will be problematic to get any power out of IMHO.

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"I couldn't wait for success, so I went ahead without it."

Back in the 70's the Champion framed Yamaha Twins used the road racer motors like the TD2 and TD3. The RD 250 will be problematic to get any power out of IMHO.

I am not familiar with that engine. The microfiche does not should reeds, is that correct? Are they the same series as the Bonanza and Catalina (I had one of each)? Were the TDs revised, and became the TZ?

I am not familiar with that engine. The microfiche does not should reeds, is that correct? Are they the same series as the Bonanza and Catalina (I had one of each)? Were the TDs revised, and became the TZ?

That's odd,I used to race shorttrack and halfmiles and quarter miles back in the day,mid 70's into the early 80's till flattrack died here.

On a halfmile the twins always smoked all comers,usually some combination of RD/aircooled roadrace parts Yamahas. Granted a person would have to know how to build and ride a twin but they are FAST.

Randy Mamola (as a kid) used to show up with 3 bikes,a mechanic or two,and his dad. 3 bikes that matched perfectly and done up to a T.
His Yamaha twin was a rocket,as were all of the expert/pro class twins.

Those twins made the neatest sound flying down the straights and lighting it up off the corners,I suppose a 360 single would be simpler,they always sounded like they were on the verge of blowing up trying to hang with the twins on a half mile.

I agree that a twin will be the cat's meow. But, the biggest thing is lack of seat time on my part. I do not really care to have a twin kill me at my first race

It COULD be more excitement then a normal person could handle,and Im sure a fast one would be maintenance intensive. A 360 could be a 1/4 mile bike,shorttrack bike,and also ride half miles. Twin would be mile or half mile,but would make all sorts of cool sounds. Starting with a DT360 is maybe not the best platform for going fast. The rare 1974 YZ360 engine always looked fast at our local shorttrack,guys yanked the engines and stuck em in Champion frames and they flew!

Too bad I sold off all my RD350 road race parts. You might've found things like the CalFab swingarm useful.

The RD250 will work fine. Find yourself a set of RD350 pipes, and I think they bolt right on. I forget the 250 carb size, but the stock 350 carbs were 28mm. Running 32mm on a 350 really woke it up with some mild porting. Any of the road race porting should work well for you and is easy to do.

What do you want, torque or hp? If you want hp, go with bigger carbs. If you want torque, stick to 28-30mm.

You may need to slice/dice the expansion chambers to both exit on the right side or you'll be dragging the left silencer.

The RD400 swingarm is longer if you want that. 250/350 wheels will work on it, but you'll need to make a spacer for the right side to hold the axle.

Get a magneto system so you can ditch the batter. I hate PVLs, and would not recommend them. Their timing curve is all wrong, and they're expensive.

There's an expansion chamber company in texas that makes flat track pipes... forget their name. Not Jemco.. there's another one.

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